This research was supported by the Natural Sciences and
Engineering Research Council of Canada (NSERC) and
Alberta's Informatics Circle of Research Excellence (iCORE).
We thank Jörg Hoffmann for making the source code of FF available,
and for kindly answering many technical questions related to FF.
We also thank the organizers of IPC-4, the reviewers of this article,
and Maria Fox, who led the reviewing process.